Ditherering to me has a definite connotation of indecisiveness and/or time wasting - I think of it at physical more than verbal I potter rather than putter.

I might also do a bit of faffing about (I'd see faffing as having a flavour of wasting time /aimlessness, whereas pottering would be unhurried but not necessarily aimless)

Blithering I have only come across as a emphasis to idiot "The man's a blithering idiot" - blather is, as amandaelizabeth says, rambling on - foolishly or repetitively.

Piddle to me is what puppies and very small children do (although more robustly (if I can use it without upsetting the filters) 'pissing about' means wasting time, messing around - If I heard someone talk about someone 'piddling about' I'd think they were using it as a euphemism for 'pissing about'.

I drive over the river Piddle fairly regularly.

Stormtreader:
Dithering to me is when youve been stressed over something like a party and cant make some teeny decision, like dithering over which flavour of cupcakes to buy - either would be fine but you just cant decide.

scotcat60:
Have just come across the word "QUIDDLE" in my old 1936 dictionary, to do a series of pointless, time-wasting jobs. Different then form pottering, when the jobs need to be done.

cwm:
I'm in the midwest, I putter about the house completely aimlessly. Cars putter along the road.

Dithering to me is a mental thing. You dither about whether to wear the red shirt with the black pumps or the black dress with the ballet flats when you go out at night.

Futzing, to me, is unnecessarily messing with. For example, if I'm puttering about, I might fold a few towels, go to wash a few dishes, just basically wander around aimlessly doing random things for a tiny bit before moving on to something else. If I was futzing about the towels, I'd unfold all of the towels in the house just to get them right.

Shea:
Grew up in the US Pacific Northwest, now live in Quebec. I'd use "putter" and "potter" interchangeably, but I can't recollect anyone ever using the terms around me where I live now, so I'm not sure what the more common term is here.